How to Write while and do while Loops in Java
while loop in Java executes one or more statements after testing the loop continuation condition at the start of each iteration. The
do while loop, however, tests the loop continuation condition after the first iteration has completed. Therefore, the
do while loop guarantees one execution of the loop logic whereas the
while does not. To understand how to code each of these loops, follow these eight steps.
- Open your text editor and type in the following Java statements.
Notice that each loop will execute five times because the loop continuation condition is
i < 5and the variable
iis initialized to 0 but pre-incremented to 1 on first reference.
- Save your file as WritewhileAnddowhileLoops.java.
- Open a command prompt and navigate to the directory containing your Java program. Then type in the command to compile the source and hit Enter.
- You are ready to test your program. Type in the command to run the Java runtime launcher and then hit Enter.
Notice each loop executes five times.
- To understand the difference between the two types of loops, modify WritewhileAnddowhileLoops.java in your text editor so that the value of
whileloop statement will not execute at all now. However, one iteration of the
do whilewill execute.
- Save your changes.
- Return to your command prompt and compile the modified source.
- Test your modified program. Type in the command to run the Java runtime launcher and then hit Enter. Notice that the
whilestatement did not execute, whereas one iteration of the
do whiledid execute.